Thread: ClickListener cannot be resolved to a type

Hi. I'm just starting to learn about inner classes. The following code is an example I followed from my book, but I still don't fully understand the explanation on lines 22 - 24:

package samsExperiments;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
 
public class InnerClassTest extends JFrame{
 
	public InnerClassTest() {
		//code that sets up the frame
		this.setTitle("TestFrame");
		this.setSize(400,100);
		this.setLocationByPlatform(true);
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		JPanel panel = new JPanel();
		this.add(panel);
 
		//code that creates the button and adds the listener
		JButton button1 = new JButton("Click me!");
		//Next, we create an object from the inner ClickListener class and assign it
		//to an ActionListener variable. This is possible because the ClickListener class
		//implements the ActionListener interface and it's actionPerformed method:
		ActionListener listener = new ClickListener();//ClickListener cannot be resolved to a type
		button1.addActionListener(listener);
 
		//display the frame window
		panel.add(button1);
		this.setVisible(true);
 
		//the inner class that implements the listener
		class ClickListener implements ActionListener{
			@Override
			public void actionPerformed(ActionEvent e) {
				System.out.println("The button was clicked!");
			}
		}//end of the inner class
 
	}//end of the outer class
}

The error on line 25 says, "ClickListener cannot be resolved to a type". I'm used to seeing an object instantiation be created from a class such as "class x = new class()".

Since when is it possible assign an object instance to a variable instead of creating one from a class? What is going on here?